I shoulda cited my source for the specs in my original post- they're from the Technical Specifications page on the Vandoren website:
    https://www.vandoren-en.com/V5-Saxophone-Mouthpieces_a48.html 
        >>> Click here to view the product datasheet
     This chart indicates that both the A20 & A25 have ML facing lengths, and 1.86mm (.073") tip openings.  Might that be a misprint? 
     Sounds like there're a lot of "alternative specs" out there.

Yes, I have looked at those same Vandoren specs.  The significant spec discepancies are not a new thing with the internet!  I really think that the only way to get the real answer is to contact Vandoren directly and ask them.

If you find out, please update this thread with the answer.

Good luck! 

OK, so I was so intrigued by the duplicate specs that I contacted Van Doren myself.  Here is the very interesting response that they sent.

"You are correct, the tip opening and facing length of the A25 and the A20 are identical.  The only difference is in the thickness of the rails.  The A20 has slightly thicker rails which does add a bit of resistance to the mouthpiece.  This can result in a mouthpiece that may be a little darker, has more resistance of attack, and can also work better with lighter reeds."

An interesting explanation, but why don't they give some hint of this in the spec sheet? 

Because they want you to use their dealer network, rather than find everything out on the internet.  One of the ways that equipment manufacturers support their knowledgable dealer network is by not puting everything out on the internet.  

I live in a place where the closest ‘good’ horn shop is a couple hour drive.  I actually waste a lot of money buying stuff on the internet that doesn’t work out because it is a 5 hour committment for me to run to the music store. Using a store really is more efficient, if you have one close by.  

I personally believe that independent music shops should be supported. They provide a valuable service.